1. Field of the Invention
Typically, high concentrations of anthelmintic compounds are required for killing parasites in their habitat within a host. In the case of intestinal nematodes, anthelmintics must be ingested or absorbed by the worms for expulsion of the parasite from the host. The absorption of the anthelmintic compound by the nematode within the host does not necessarily result in ovicidal activity. Animals being treated are placed in a different pasture or area than before treatment to avoid nematodal ova. There is a need for products which control nematodal ova in the environment of the animal.
This invention relates to a method of controlling nematodes by contacting the eggs and larvae thereof with a bacterial toxin having ovicidal and larvicidal activity.
2. Description of the Prior Art
Luthy et al. [Pharmacol. Therapeut. 13: 257-283 (1981)] teach that various Bacillus species have been recognized as insecticidal pathogens, with Bacillus thuringiensis being the most widely used, commercially available bacterium for insect control. According to Burgess [Parasitol. 84: 79-117 (1982)] a number of isolates of B. thuringiensis have been reported. Some of the earlier bacterial varieties were active against lepidopteran insects, more recent isolates of B. thuringiensis show activity toward nonlepidopteran insect species. For example, B.t. israelensis is active against dipteran insects, such as mosquito species and blackfly larvae. Other varieties of B. thuringiensis also show promise against mosquito species which play an important role in the transmission of parasitic diseases of man. Favret et al. [J. Invertebr. Pathol. 45: 195-203 (1985)] suggest that a heat-resistant toxin from B. laterosporus is pathogenic to mosquito larvae. They also report that this pathogenicity is associated with the cell mass rather than the culture supernatant or bacterial spores.
Despite the use of microbial species and their products as insecticides, there is not much information available about the microbial control of nematodes. Ciordia et al. [J. Parasitol. 47: Abstract 41 (1961)] describe the mixing of spores of B. thuringiensis with cow feces that contain eggs of Cooperia punctata, C. oncophora, and Ostertagia ostertagi and recover reduced numbers of third-stage larvae as the concentration of spores per gram of feces increased clearly showing that some strains of B. thuringiensis have nematicidal activity.
Bottjer et al. [Exper. Parasitol. 60: 239-244 (1985)] teach that a large number of strains of B. thuringiensis and their toxins were effective in killing the ruminant nematode Trichostrongylus colubriformis and other nematodes. All the tests strains of B. thuringiensis were toxic to T. colubriformis eggs. In U.S. Pat. No. 4,781,922, Bone discloses a method of controlling nematodes in host animals with a toxin from B. sphaericus having ovicidal activity.